Injection molding involves the transfer of a molten material into a mold, typically at high pressures. Plastic injection molding is one such process, in which an injection unit melts pelletized plastic into molten plastic before injecting the molten plastic into a closed mold. In its most basic configuration, the mold includes two halves, a core half and a cavity half, which cooperate to define a mold cavity in the desired shape of a single article. The molten plastic cools and solidifies between the mold halves, and is then ejected from the mold cavity as the finished article.
To carefully regulate the flow of molten plastic into the mold cavity, typically as a controlled-volume shot of molten plastic, the injection unit can include a series of valve gates. Each valve gate can be seated over an opening in the mold to selectively allow the flow of molten plastic into the mold cavity. Known valve gates include a valve gate pin disposed within a passageway that has a narrow terminal end adjacent to the mold opening. The valve gate pin moves away from and toward the terminal end of the passageway to open and close the valve gate, respectively, which allows the introduction of the molten material into the mold cavity. This process is repeated for each successive shot of molten plastic.
Movement of the valve gate pin is typically performed by actuators under control of a processor. In many injection molding operations, the actuators must overcome injection pressures that range from 2,000 psi to at least 25,000 psi, dependent upon a variety of factors, including the density of the molten plastic. Existing actuators include pneumatic actuators and hydraulic actuators. However, these actuators require a source of compressed air or hydraulic fluid, which may lose pressure over the course of an injection molding operation. While electromechanical actuators are also known, there remains a continued need for an improved electromechanical actuator with increased reliability, pressure resistance, and precision over existing systems.